Datasheet

ΔI
L
I = I +
L
OUT
2
V V
OUT OUT
x 1 -
η V x η
IN
I = I +
L
OUT
2 x x Lf
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TPS62090, TPS62091
TPS62092, TPS62093
www.ti.com SLVSAW2A –MARCH 2012–REVISED MARCH 2012
Inductor Selection
The inductor selection is affected by several parameter like inductor ripple current, output voltage ripple,
transition point into Power Save Mode, and efficiency. See Table 4 for typical inductors.
Table 4. Inductor Selection
INDUCTOR VALUE COMPONENT SUPPLIER SIZE (LxWxH mm) Isat/DCR
0.6 µH Coilcraft XAL4012-601 4 x 4 x 2.1 7.1A/9.5 mΩ
1 µH Coilcraft XAL4020-102 4 x 4 x 2.1 5.9A/13.2 mΩ
1 µH Coilcraft XFL4020-102 4 x 4 x 2.1 5.1 A/10.8 mΩ
0.47 µH TOKO DFE252012 R47 2.5 x 2 x 1.2 3.7A/39 mΩ
1 µH TOKO DFE252012 1R0 2.5 x 2 x 1.2 3.0A/59 mΩ
0.68 µH TOKO DFE322512 R68 3.2 x 2.5 x 1.2 3.5A/37 mΩ
1 µH TOKO DFE322512 1R0 3.2 x 2.5 x 1.2 3.1A/45 mΩ
In addition, the inductor has to be rated for the appropriate saturation current and DC resistance (DCR). The
inductor needs to be rated for a saturation current as high as the typical switch current limit, of 4.6 A or according
to Equation 7 and Equation 8. Equation 7 and Equation 8 calculate the maximum inductor current under static
load conditions. The formula takes the converter efficiency into account. The converter efficiency can be taken
from the data sheet graph`s or 80% can be used as a conservative approach. The calculation must be done for
the maximum input voltage where the peak switch current is highest.
(7)
(8)
where
ƒ = Converter switching frequency (typical 2.8 MHz or 1.4 MHz)
L = Selected inductor value
η = Estimated converter efficiency (use the number from the efficiency curves or 0.80 as an conservative
assumption)
Note: The calculation must be done for the maximum input voltage of the application
Calculating the maximum inductor current using the actual operating conditions gives the minimum saturation
current. A margin of 20% needs to be added to cover for load transients during operation.
Input and Output Capacitor Selection
For best output and input voltage filtering, low ESR ceramic capacitors are recommended. The input capacitor
minimizes input voltage ripple, suppresses input voltage spikes and provides a stable system rail for the device.
A 22 µF or larger input capacitor is recommended for 1.4 MHz operation frequency. For 2.8 MHz operation
frequence a 10 µF input capacitor or larger is recommended. The output capacitor value can range from 10 µF
up to 150 µF and beyond. The recommended typical output capacitor value is 22 µF and can vary over a wide
range as outline in the output filter selection table.
Table 5. Input Capacitor Selection
INPUT CAPACITOR COMMENT
10 µF FREQ=low, f=2.8 MHz
22 µF FREQ=high, f=1.4 MHz
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